Undocumented, but the Spanner accept this value at least.

AddColumn is ADD COLUMN clause in ALTER TABLE.

AddRowDeletionPolicy is ADD ROW DELETION POLICY clause in ALTER TABLE.

AddStoredColumn is ADD STORED COLUMN clause in ALTER INDEX.

AddTableConstraint is ADD table_constraint clause in ALTER TABLE.

Alias is aliased expression by AS clause in SELECT result columns list.

AlterChangeStream is ALTER CHANGE STREAM statement node.

AlterColumn is ALTER COLUMN clause in ALTER TABLE.

AlterColumnSet is ALTER COLUMN SET clause in ALTER TABLE.

AlterIndex is ALTER INDEX statement node.

AlterTable is ALTER TABLE statement node.

AraryLiteral is array literal node.

ArraySchemaType is array type node in schema.

ArraySubQuery is subquery in ARRAY call.

ArrayType is array type node.

AsAlias is AS clause node for general purpose.

AtTimeZone is AT TIME ZONE clause in EXTRACT call.

BetweenExpr is BETWEEN expression node.

BinaryExpr is binary operator expression node.

BoolLiteral is boolean literal node.

BytesLiteral is bytes literal node.

CallExpr is function call expression node.

CaseElse is ELSE clause in CASE expression.

CaseExpr is CASE expression node.

CaseWhen is WHEN clause in CASE expression.

CastExpr is CAST call expression node.

CastIntValue is cast call in integer value context.

CasrNumValue is cast call in number value context.

ChangeStreamDropForAll is DROP FOR ALL node in ALTER CHANGE STREAM DROP FOR ALL.

ChangeStreamForAll is FOR ALL node in CREATE CHANGE STREAM FOR ALL.

ChangeStreamForTable table node in CREATE CHANGE STREAM SET FOR {{.TableName | sql}}{{if .Columns}}({{.Columns | sqlJoin ","}}){{end}}.

ChangeStreamForTables is FOR tables node in CREATE CHANGE STREAM FOR {{.Tables | sqlJoin ","}}.

ChangeStreamOptions is OPTIONS clause node in CREATE CHANGE STREAM.

ChangeStreamOptionsRecord is OPTIONS record node.

ChangeStreamSetFor is SET FOR tables node in ALTER CHANGE STREAM SET FOR {{.For | sql}}.

ChangeStreamSetOptions is SET OPTIONS node in ALTER CHANGE STREAM SET {{.Options | sql}}.

Check is check constraint in CREATE TABLE and ALTER TABLE.

Cluster is INTERLEAVE IN PARENT clause in CREATE TABLE.

Collate is COLLATE clause node in ORDER BY item.

ColumnDef is column definition in CREATE TABLE.

ColumnDefaultExpr is a default value expression for the column.

ColumnDefOption is options for column definition.

CompoundQuery is query statement node compounded by set operators.

CountStarExpr is node just for COUNT(*).

CreateChangeStream is CREATE CHANGE STREAM statement node.

CreateDatabase is CREATE DATABASE statement node.

CreateIndex is CREATE INDEX statement node.

CreateRole is CREATE ROLE statement node.

CreateRowDeletionPolicy is ROW DELETION POLICY clause in CREATE TABLE.

CreateSequence is CREATE SEQUENCE statement node.

CreateTable is CREATE TABLE statement node.

CreateView is CREATE VIEW statement node.

CTE is common table expression node.

DateLiteral is date literal node.

DefaultExpr is DEFAULT or Expr.

Delete is DELETE statement.

DeletePrivilege is DELETE ON TABLE privilege node in GRANT and REVOKE.

DotStar is expression with * in SELECT result columns list.

DropChangeStream is DROP CHANGE STREAM statement node.

DropColumn is DROP COLUMN clause in ALTER TABLE.

DropConstraint is DROP CONSTRAINT clause in ALTER TABLE.

DropIndex is DROP INDEX statement node.

DropRole is DROP ROLE statement node.

DropRowDeletionPolicy is DROP ROW DELETION POLICY clause in ALTER TABLE.

DropStoredColumn is DROP STORED COLUMN clause in ALTER INDEX.

DropTable is DROP TABLE statement node.

ExecutePrivilegeOnTableFunction is EXECUTE ON TABLE FUNCTION privilege node in GRANT and REVOKE.

ExistsSubQuery is subquery in EXISTS call.

ExprArg is argument of the generic function call.

ExprSelectItem is Expr wrapper for SelectItem.

ExtractExpr is EXTRACT call expression node.

FloatLiteral is floating point number literal node.

ForeignKey is foreign key specifier in CREATE TABLE and ALTER TABLE.

From is FROM clause node.

GeneratedColumnExpr is generated column expression.

Grant is GRANT statement node.

GroupBy is GROUP BY clause node.

Having is HAVING clause node.

Hint is hint node.

HintRecord is hint record node.

Ident is identifier node.

IndexExpr is array item access expression node.

IndexKey is index key specifier in CREATE TABLE and CREATE INDEX.

InExpr is IN expression node.

Insert is INSERT statement node.

InsertPrivilege is INSERT ON TABLE privilege node in GRANT and REVOKE.

InterleaveIn is INTERLEAVE IN clause in CREATE INDEX.

IntervalArg is argument of date function call.

IntLiteral is integer literal node.

IsBoolExpr is IS TRUE/FALSE expression node.

IsNullExpr is IS NULL expression node.

Join is JOIN expression.

Limit is LIMIT clause node.

NullLiteral is just NULL literal.

NumericLiteral is numeric literal node.

Offset is OFFSET clause node in LIMIT clause.

On is ON condition of JOIN expression.

OrderBy is ORDER BY clause node.

OrderByItem is expression node in ORDER BY clause list.

Param is Query parameter node.

ParenExpr is parenthesized expression node.

ParenTableExpr is parenthesized JOIN expression.

Path is dot-chained identifier list.

PrivilegeOnTable is ON TABLE privilege node in GRANT and REVOKE.

QueryStatement is query statement node.

ReplaceRowDeletionPolicy is REPLACE ROW DELETION POLICY clause in ALTER TABLE.

Revoke is REVOKE statement node.

RolePrivilege is ROLE privilege node in GRANT and REVOKE.

RowDeletionPolicy is ROW DELETION POLICY clause.

ScalarSchemaType is scalar type node in schema.

ScalarSubQuery is subquery in expression.

Select is SELECT statement node.

SelectorExpr is struct field access expression node.

SelectPrivilege is SELECT ON TABLE privilege node in GRANT and REVOKE.

SelectPrivilegeOnView is SELECT ON VIEW privilege node in GRANT and REVOKE.

SequenceArg is argument of sequence function call.

SequenceOption is option for CREATE SEQUENCE.

SetOnDelete is SET ON DELETE clause in ALTER TABLE.

SimpleType is type node having no parameter like INT64, STRING.

SizedSchemaType is sized type node in schema.

Star is a single * in SELECT result columns list.

Storing is STORING clause in CREATE INDEX.

StringLiteral is string literal node.

StructField is field in struct type node.

StructLiteral is struct literal node.

StructType is struct type node.

SubQuery is subquery statement node.

SubQueryInCondition is subquery at IN condition.

SubQueryInput is query clause in INSERT.

SubQueryTableExpr is subquery inside JOIN expression.

TableConstraint is table constraint in CREATE TABLE and ALTER TABLE.

TableName is table name node in FROM clause.

TableSample is TABLESAMPLE clause node.

TableSampleSize is size part of TABLESAMPLE clause.

TimestampLiteral is timestamp literal node.

UnaryExpr is unary operator expression node.

Unnest is UNNEST call in FROM clause.

UnnestInCondition is UNNEST call at IN condition.

Update is UPDATE statement.

UpdateItem is SET clause items in UPDATE.

UpdatePrivilege is UPDATE ON TABLE privilege node in GRANT and REVOKE.

Using is Using condition of JOIN expression.

ValuesInCondition is parenthesized values at IN condition.

ValuesInput is VALUES clause in INSERT.

ValuesRow is row values of VALUES clause.

Where is WHERE clause node.

With is with clause node.

WithOffset is WITH OFFSET clause node after UNNEST call.

Arg represents argument of function call.

ChangeStreamAlteration represents ALTER CHANGE STREAM action.

ChangeStreamFor represents FOR clause in CREATE/ALTER CHANGE STREAM statement.

Constraint represents table constraint of CONSTARINT clause.

DDL represents data definition language in SQL.

DML represents data manipulation language in SQL.

Expr repersents an expression in SQL.

InCondition is right-side value of IN operator.

IndexAlteration represents ALTER INDEX action.

InsertInput represents input values of INSERT statement.

IntValue represents integer values in SQL.

JoinCondition represents condition part of JOIN expression.

Node is base interface of Spanner SQL AST nodes.

NumValue represents number values in SQL.

Privilege represents privileges specified by GRANT and REVOKE.

QueryExpr represents set operator operands.

SchemaType represents types for schema.

SelectItem represents expression in SELECT clause result columns list.

Statement represents toplevel statement node of Spanner SQL.

StringValue represents string value in SQL.

TableAlteration represents ALTER TABLE action.

TableExpr represents JOIN operands.

TablePrivilege represents privileges on table.

Type represents type node.